on a ZCS 6.0.2 OSS system (64-bit), one of internal users send an email with 5 MB attachment to the distribution list for all interal staff(~ 1000 users).

after then, users found they have problem to download email via pop3 , their outlook express show the process of email downloading, but can not complete. obviously, it's stuck in that email with 5MB attachment, they have to login web interface and remove that email, then everything goes fine.

the other users (like admin and some system accounts) don't have this problem, cause they didn't belong to that distribution list.

Checking the mailbox.log for that period of time, i didn't find anything obvious, just found this I/O error message below. Does anyone see this before and how to solve ( or avoid) this kind of issue? Thanks.